The invention relates to an apparatus for producing ozone comprising two spaced electrodes having conductors for connection to a voltage source of alternating amplitude and comprising at least one electrically-insulating separator wall, preferably of glass, between these electrodes and having at one side an ozonisation chamber connected to an inlet for an oxygen-charged medium, particularly air, and with an outlet for the ozone-enriched medium, together with a method of producing ozone by means of an apparatus of this nature.
Ozone is generally formed by the action of oxygen atoms on oxygen molecules. The splitting of an oxygen molecule can for example be achieved by applying electrical, optical chemical or thermal energy. The invention relates in particular to the splitting of oxygen by means of electrical energy, the voltage applied between the two electrodes (electrode and counterelectrode) having an amplitude which varies with time, for example an alternating voltage or a pulsating direct voltage.
Known apparatus of the type first set forth above derive for the most part from the "Siemens Ozonisator". This consists in principle of two interfitted, coaxial glass tubes with a tubular ozonisation chamber between them. Water is disposed at least at one side of a separator wall facing away from the ozonisation chamber.
Although apparatus of this nature, which in the meantime have been much improved, have been extensively used on a large scale for water treatment in the preparation of drinking water, for purification and sterilization of swimming baths, in the production of oxygen carriers for rocket impellants etc., the degree of efficiency thereof is not yet satisfactory and lies at this time, even in the case of the best plants, still less than 50% of the degree of efficiency which is theoretically achievable, even starting from the theoretically possible energy consumption of about 2.4 W.h per gramme ozone. Typically the degree of efficiency of known apparatus of the kind first set forth above is about 25%. The major proportion of the energy applied is converted into heat which has to be dissipated by cooling water. A temperature increase of the oxygen-containing medium which is fed into the inlet of the ozonisation chamber to values over 38.degree. Celsius at the outlet must be prevented because as temperature increases the liklihood of decomposition of the ozone is raised.
Further, the priming and operating voltages of the known apparatus reach relatively high values, particularly frequently above 20 kilovolts, to make the yield a maximum in the parameters quoted. Insulation problems arise where there are high priming and operating voltages of the nature set out and these are further increased with the presence of cooling water and steam. Additionally, also detrimental, is the formation of nitrous oxides which notoriously appear at operating voltages over 15 kilovolt and in particular are damaging in water treatment by means of ozone because nitrous acid and subsequently nitric acid may be formed when the ozone together with the unwnted nitrous oxides are introduced into water. Coolant problems may also arise.
Finally ozone production which on the face of it is small with the known apparatus has to be relatively large in size. This in turn increases the costs of manufacture and the costs involved in practical terms.
It has been previously known to apply to a Siemens Ozonisator instead of a normally used alternating voltage a voltage of varying amplitude, and in particular a pulsed voltage. It has been found that because of the increased number of electrical excitations per unit time the yield in ozone is increased. The higher number of excitation phenomena possibly may be attributed to a greater promise of ozone formation or a longer period of dwell of the split oxygen molecular in their atomic condition. The introduction of voltages with frequency in the lower frequency range leads however, in the case of the known apparatus, to high electrical losses, particularly in the ozone producing apparatus device itself so that in toto higher frequencies in the voltage applied to the electrodes gives no gain to the ozonisation appliances with alternating voltage or for operation when pulsating direct voltage could not therefore be successful.